The organ donor family members' perception of stressful situations during the organ donation experience

The purpose of this study was to determine what the individual organ/tissue donor family members appraised as most stressful during the anticipation, confrontation and post-confrontation stages of the organ-donation process. The Lazarus and Folkman stress and coping theory guided the development and interpretation of the study. Family members who had lost a loved one suddenly and consented to donation in 1988 were interviewed. Data were analysed by means of content analysis. Findings showed that family members appraised different types of stressful situations during the three stages. The most frequently reported stressful situations centred around the threat of losing a loved one, confirmation of brain death, failure of the health professionals to identify the loved one as a potential donor and to approach the family regarding organ donation, and adjusting to the many changes associated with the loss. Significantly, five families requested donation, while two readily consented when approached. All family members reported that organ donation had helped with their grief. The findings of this study contribute to the development of knowledge required to guide nursing interventions to provide sensitive care to donors and their families.

IL-1 production by human thymic dendritic cells: studies on the interrelation with DC accessory function

Thymic dendritic cells (DC) have been proposed to play a critical role in the generation of immunocompetent T lymphocytes. Since IL-1 is widely considered to be an important second signal in T cell stimulation, we have studied the ability of isolated human thymic DC to produce IL-1. Using the EL4/CTLL conversion assay standardized with recombinant IL-1 beta (rIL-1 beta), we demonstrate that upon LPS-stimulation thymic DC produce small amounts of IL-1 as compared to peripheral blood monocytes (PBM). In contrast with PBM, DC IL-1 production is not influenced by indomethacin. IL-1 activity was detected in the supernatants of DC cultures from all thymuses tested, although quantitative variability was noted among individual thymic donors. The specificity of the active factor was confirmed by neutralization assays with anti-IL-1 beta mAb. On the other hand, we demonstrate that rIL-1 beta cannot substitute for nor amplify the accessory function of thymic DC and that anti-IL-1 beta mAb fails to block the DC accessory function. Thus we conclude that IL-1 beta might not be a major factor for the efficient DC accessory function toward mature thymocytes recently demonstrated in our laboratory. Of interest, IL-1 beta was also detected in the supernatants of DC-thymocyte cocultures in the absence of mitogenic factor, suggesting that thymocyte contacts can constitute a sufficient signal to induce DC to produce IL-1. These observations indicate that human thymic DC represent an intrathymic source of IL-1 whose role in thymocyte proliferation or maturation remains to be understood.

Accessory function of human thymic dendritic cells in Con A-induced proliferation of autologous thymocyte subsets

Human thymic dendritic cells (DC) have previously been shown to be intimately associated with thymocytes in situ and in culture. We report that thymic DC express LFA-3 and ICAM-1 adhesion molecules and may spontaneously associate with autologous thymocytes within mitogen-independent clusters. Moreover, the accessory activity of isolated human thymic DC was investigated in Con A-stimulation assays. By proliferation experiments, measured as [3H]TdR incorporation, we demonstrated that irradiated thymic DC strongly increase the mitogen-induced activation of autologous PBL as well as of unfractionated thymocytes. More interestingly, in coculture assays performed with purified thymocyte subsets, we have found that thymic DC greatly enhance the Con A proliferation of CD1- CD3bright thymocytes whereas the accessory activity toward the CD1+ CD3- thymocytes was very weak. Inhibition experiments demonstrated that the DC accessory activity is inhibited by anti-DR-related and anti-IL-2R mAb. However, blocking assays with anti-CD11b, anti-CD11c, anti-LFA-3, and anti-ICAM1 mAb showed that the accessory function obtained is similar to that with untreated cultures. We conclude that isolated human thymic DC may present potent DR- and IL-2-dependent accessory activity mainly directed toward the CD1- CD3bright thymocyte subpopulation, suggesting that thymic DC may be involved in the in vivo proliferation of mature thymocytes.

Accessory function of human thymic dendritic cells in Con A-induced proliferation of autologous thymocyte subsets

Human thymic dendritic cells (DC) have previously been shown to be intimately associated with thymocytes in situ and in culture. We report that thymic DC express LFA-3 and ICAM-1 adhesion molecules and may spontaneously associate with autologous thymocytes within mitogen-independent clusters. Moreover, the accessory activity of isolated human thymic DC was investigated in Con A-stimulation assays. By proliferation experiments, measured as [3H]TdR incorporation, we demonstrated that irradiated thymic DC strongly increase the mitogen-induced activation of autologous PBL as well as of unfractionated thymocytes. More interestingly, in coculture assays performed with purified thymocyte subsets, we have found that thymic DC greatly enhance the Con A proliferation of CD1- CD3bright thymocytes whereas the accessory activity toward the CD1+ CD3- thymocytes was very weak. Inhibition experiments demonstrated that the DC accessory activity is inhibited by anti-DR-related and anti-IL-2R mAb. However, blocking assays with anti-CD11b, anti-CD11c, anti-LFA-3, and anti-ICAM1 mAb showed that the accessory function obtained is similar to that with untreated cultures. We conclude that isolated human thymic DC may present potent DR- and IL-2-dependent accessory activity mainly directed toward the CD1- CD3bright thymocyte subpopulation, suggesting that thymic DC may be involved in the in vivo proliferation of mature thymocytes.

Killing of Mycobacterium smegmatis by macrophages from genetically susceptible and resistant mice

The bactericidal function of macrophages was investigated in congenic mice expressing the phenotype of susceptibility (B10.A, Bcgs) or resistance (B10.ABcgr) to mycobacterial infection. When splenic and peritoneal macrophages from these two mouse strains were infected in vitro with Mycobacterium smegmatis, the Bcgr macrophages were shown to inactivate M. smegmatis more efficiently than their Bcgs congenic counterparts. The mechanisms of this superior antimycobacterial activity was studied further. Addition of catalase did not abolish killing to a significant degree in either allelic type of macrophage, suggesting that hydrogen peroxide production was not involved in the killing activity controlled by the Bcg gene. Activation of Bcgs macrophages by exposure to crude lymphokines rendered them equally as efficient as their Bcgr counterparts in their capacity to destroy M. smegmatis. This finding suggests that both the genetically resistant and susceptible macrophages have the potential to kill M. smegmatis in vitro. This potential is expressed constitutively by the Bcgr but not Bcgs macrophages and can be induced, by lymphokine treatment, in the Bcgs macrophages. In a final set of experiments, the macrophage killing of M. smegmatis was evaluated as a test system to type for the Bcg gene allelic type in vitro, using a set of AXB and BXA recombinant inbred strains of mice. Results obtained show that typing of AXB/BXA recombinant inbred strains for the trait of bactericidal activity vs. M. smegmatis in vitro revealed a perfect match with the strain distribution pattern of resistance/susceptibility to Mycobacterium bovis BCG in vivo.

The state of cellular differentiation determines the activity of the adenovirus E1A enhancer element: evidence for negative regulation of enhancer function

Most of the eucaryotic enhancer elements so far described consist of multiple DNA binding sites for proteins that act either synergistically or antagonistically to modulate the rate of transcription. In this report, we show that the activity of the adenovirus E1A enhancer element is suppressed in virus-infected undifferentiated rodent fetal fibroblast cells (CREF and F111 cells) and primary rat liver hepatocytes that have lost their fully differentiated phenotype (dedifferentiated). This contrasts with the results obtained for virus-infected differentiated or partially dedifferentiated rodent hepatocytes or hepatoma cell lines and human HeLa cells, in which deletion of the E1A enhancer domain greatly reduces the rate of E1A gene transcription. An in vitro quantitation of the nuclear proteins (from HeLa and CREF cells) that interact with and modulate the activity of the E1A enhancer revealed similar binding activities for the E2f and ATF proteins. However, an AP3-like (phi AP3) activity was present at a 10- to 20-fold higher concentration in CREF cells than in HeLa cells, and removal of this phi AP3-binding site on the viral genome resulted in an increase in the rate of E1A gene transcription in virus-infected CREF cells. Together, these results demonstrated that the factors which positively regulate enhancer function were present in CREF cells and that the phi AP3 factor was acting to suppress the activity of the E1A enhancer. Furthermore, the level of this factor was found to increase to even higher levels in CREF cells treated with 12-O-tetradecanoylphorbol-13-acetate, and this induction resulted in a further suppression in the rate of E1A gene transcription. On the basis of these observations, we propose that E1A expression is negatively regulated by the phi AP3 factor in undifferentiated rodent fetal fibroblast cells and that this could be an important mechanism that distinguishes between establishment of the differentiated cell versus transformed cell phenotypes.

Cis effect of the type 5 adenovirus E1A gene enhancer element on cellular transformation

Mutants of type 5 adenovirus that lack all or part of the early region 1A (E1A) gene enhancer element transform rodent embryo fibroblast (CREF) cells at higher efficiencies than wild-type virus. An analysis of viral E1A cytoplasmic mRNA levels in mutant and wild-type virus-infected CREF cells revealed no differences in the levels of the E1A mRNAs. This implies that a decrease in the rate of viral E1A gene expression was not responsible for the transforming properties of the enhancer-less viruses. Unlike wild-type virus, however, the mutant viruses were able to replicate their genomes in the normally nonpermissive CREF cells. This change in viral DNA template concentration further resulted in an increase in early gene mRNA concentrations in mutant-virus-infected CREF cells. These studies suggest several possible mechanisms that could be responsible for the increased transforming potentials of these viruses, including 1) a cis effect of removing the viral E1A enhancer element on the efficiency of viral DNA integration, 2) viral DNA replication, or 3) an increase in the levels of the viral E1A and E1B mRNAs owing to viral DNA replication in the virus-infected CREF cells.

Human thymic dendritic cell-thymocyte association: ultrastructural cell phenotype analysis

In rodent thymus, associations between dendritic cells (DC) and thymocytes have been suggested to be implicated in differentiation and/or maturation processes. In this study, we report intimate associations formed between human thymic DC and thymocytes in culture and we analyze their ultrastructural cell phenotype. Observations by phase contrast microscopy showed that DC present long and thin dendrites and bind many thymocytes. Transmission (TEM) and scanning electron microscopy (SEM) revealed that both cellular populations were in close connection and tight membrane contact could be observed. The phenotype of DC and attached thymocytes was characterized with a series of monoclonal antibodies by protein A-gold TEM and SEM immunolabelings. Quantitative evaluation of immunolabeling (number of gold granules/microns of cellular membrane) suggests the presence of two subpopulations of CD1+ thymic DC (strong and weak), whereas this discrepancy is not observed in DR+ and CD4+ DC populations. On the other hand, the majority of thymocytes bound to DC strongly express the CD1, CD4, CD8 and CD2 antigens and weakly the CD3 antigen, indicating that they represent double-positive immature thymocytes. Uniform distribution of DC and thymocytes membrane antigens was confirmed with a backscattered SEM study. This morphological and immunolabeling TEM and SEM analysis demonstrates that human thymic DC may form associations with CD4+CD8+CD3weak thymocytes and raises questions about their physiological relationship.

Retention and expression of the left end subfragment of the herpes simplex virus type 2 BglII N DNA fragment do not correlate with tumorigenic conversion of NIH 3T3 cells

Cotransfection experiments have been carried out using recombinant plasmids pAG60, conferring resistance to antibiotic G418, and pXho3 which contains the left end subfragment (map coordinates 0.583 to 0.596) of the transforming herpes simplex virus type 2 BglII N DNA fragment and encodes the 36K polypeptide associated with the viral ribonucleotide reductase activity. Several NIH 3T3 cell clones resistant to G418 and having morphological changes commonly observed for transformed NIH 3T3 cells were isolated and examined for the presence and stable retention of the viral sequences. Seven of the clones that retained the transfected viral sequences were analysed for the expression of the 36K polypeptide and the tumorigenic phenotype. The results gathered from these studies show that neither the retention of the viral DNA nor the expression of the 36K polypeptide correlated with tumorigenic conversion of these cells.

Purification and characterization of a methionine-specific aminopeptidase from Salmonella typhimurium

An aminopeptidase specific for methionine (peptidase M) has been purified from wild-type and mutant Salmonella typhimurium strains. Recombinant peptidase M was also purified from Escherichia coli. These preparations were characterized with respect to their physicochemical properties using analytical ultracentrifugation, SDS/PAGE, isoelectric focusing, titration curve analysis, amino acid analysis, N-and C-terminal sequencing and various spectroscopic methods. Peptidase M activity is stimulated by Co2+, in agreement with previous studies using crude extracts of Salmonella. The purified preparations did not contain significant amounts of any metal. Enzymically important metal is loosely associated and lost during enzyme purification. Peptidase M was shown to contain seven free sulphydryl residues none of which are involved in either intra-or inter-molecular disulphide bonds. Most appear solvent-accessible as evidenced by their reactivity under native conditions. Limited modification of the sulphydryl residues with either iodoacetamide or 5,5'-dithiobis(2-nitrobenzoic acid) led to inactivation. Several cysteines were shown to be labelled to various degrees by peptide mapping of inactivated S-[14C]carboxymethylated protein. Whether cysteine modification affects enzymic activity directly (blocking an active site) or indirectly (by causing conformational change) remains to be established.

Pleiotropic effects of the Bcg gene. II. Genetic restriction of responses to mitogens and allogeneic targets

The response of Bcgr and Bcgs spleen cells to allogeneic Ag, mitogens, and in a system of oxidative mitogenesis using neuraminidase and galactose oxidase was investigated in two Bcg congenic systems. The Bcgr macrophages supported the MLR across H-2 barrier much better than the Bcgs macrophages. At sub-optimal or optimal doses of mitogens Bcgr mice were higher responders than their Bcgs counterparts. The superior response of Bcgr spleen cells to Con A was further investigated with the aim of identifying the population expressing this phenotype. T cells of either Bcgr or Bcgs type showed equal ability to respond to Con A in the presence of macrophages. Purified splenic macrophages from Bcgr mice contained a significantly greater percentage of Ia+-bearing macrophages compared to Bcgs mice. Splenic macrophages of the Bcgr type were more efficient than their Bcgs counterparts at restoring the Con A response of accessory cell-depleted spleen cells. Resident peritoneal macrophages as well as splenic dendritic cells from Bcgr and Bcgs mice were equally efficient at restoring this response. Glutaraldehyde-fixed Bcgr splenic macrophages were shown to be more efficient than the Bcgs cells at replenishing the response of Con A-unresponsive spleen cells when supplemented with IL-1.

Pleiotropic effects of the Bcg gene. II. Genetic restriction of responses to mitogens and allogeneic targets

The response of Bcgr and Bcgs spleen cells to allogeneic Ag, mitogens, and in a system of oxidative mitogenesis using neuraminidase and galactose oxidase was investigated in two Bcg congenic systems. The Bcgr macrophages supported the MLR across H-2 barrier much better than the Bcgs macrophages. At sub-optimal or optimal doses of mitogens Bcgr mice were higher responders than their Bcgs counterparts. The superior response of Bcgr spleen cells to Con A was further investigated with the aim of identifying the population expressing this phenotype. T cells of either Bcgr or Bcgs type showed equal ability to respond to Con A in the presence of macrophages. Purified splenic macrophages from Bcgr mice contained a significantly greater percentage of Ia+-bearing macrophages compared to Bcgs mice. Splenic macrophages of the Bcgr type were more efficient than their Bcgs counterparts at restoring the Con A response of accessory cell-depleted spleen cells. Resident peritoneal macrophages as well as splenic dendritic cells from Bcgr and Bcgs mice were equally efficient at restoring this response. Glutaraldehyde-fixed Bcgr splenic macrophages were shown to be more efficient than the Bcgs cells at replenishing the response of Con A-unresponsive spleen cells when supplemented with IL-1.

Genetics of resistance to infection with Candida albicans in mice

To determine differences in susceptibility, 234 naive mice including xid and beige mutants were infected intravenously with Candida albicans and monitored with survival analysis and quantitative culture of the kidneys. By using survival time as the criterion, animals of seven inbred strains were separated into three groups. C3H/HeJ and Dw/+ were most susceptible; C57BR/cdJ, BRVR and CBA/N (xid) were intermediate in susceptibility; C57BL/KsJ and C57BL/6J were least susceptible. Mean survival times (MST) were markedly influenced by the number of Candida cells injected while the ranking of mouse strains by survival alone was unchanged. There was a dissimilar behaviour of the strains to produce organ weight changes in response to infection when compared with uninfected mice which were matched for age and genetic lineage. Black mice had lower colony forming units (CFU) per mg of tissue at the time of death than animals of other genetic lineage. Nevertheless, the finding that MST and CFU studies were loosely correlated in a few strains of mice indicated that the proliferation of the fungus in the kidneys was not always the major cause of death. The beige mutation was found to determine an increased susceptibility to systemic Candida infection. The differences in survival for beige and nonbeige mice were influenced by the genetic lineage of the host, being much greater in the C57BL/6 strain (36.7 days) than in the C3H/He strain (5 days). C57BL/6 beige-J had significantly higher CFU per organ and per unit of weight than C57BL/6 +/+ mice. These data evinced an important contribution of host genetic factors to resistance to systemic candidiasis. It is suggested that innate resistance genes regulate the differentiation in the bone marrow and the function of cells of granulocyte-macrophage lineage.

Pleiotropic effects of the Bcg gene: III. Respiratory burst in Bcg-congenic macrophages

Macrophage respiratory burst, as assessed by H2O2 and O2- production, and HMS and chemiluminescence activity was investigated in a variety of conditions in macrophages from Bcg-congenic mice. Measurement of HMS and chemiluminescence in splenic macrophages challenged in vitro with BCG showed that the Bcgr cells were more stimulated by the challenge than their Bcgs counterparts. H2O2 production was measured in Bcgr and Bcgs splenic macrophages. PMA-triggering and LK-triggering were shown to stimulate a similar degree of H2O2 production Bcgr and Bcgs macrophages. In contrast, in vitro phagocytosis of BCG was shown to trigger superior production of H2O2 and O2- in the Bcgr splenic macrophages as compared to their Bcgs congenics. Finally, following the in vivo infection with BCG Montreal, Bcgr splenic macrophages were superior producers of H2O2 (both spontaneous and PMA-triggered) in the early phase of infection.

Human thymic dendritic cells. Characterization, isolation and functional assays

The phenotypic analysis of human thymic dentritic cells (DC) in culture and in purified suspensions has been studied with light and electron microscopic (EM) immunolabelling techniques. Using a series of monoclonal antibodies (mAb) and a protein A-gold technique, we demonstrated that DR- and T6-positive cultured DC strongly bind the 9.3F10 mAb, an anti-DR-related antibody produced against human blood DC, and weakly express the T4 antigen, a membrane marker shared by Langerhan's cells (LC). On the other hand, thymic-cultured DC are negative for the other T-cell and monocyte-macrophage antigens. These results support the hypothesis that human thymic DC may be related to blood DC and epidermal LC. Moreover DC, unlike thymic macrophages, do not phagocytose latex particles, opsonized sheep red blood cells (SRBC) or Candida albicans. An efficient two-step technique of isolation, using a Percoll density gradient followed by an indirect panning technique, yields a purified (70-80%) thymic DC population, OKIa1-, 9.3F10- and OKT6-positive and esterase-negative. Immunolabelling and electron microscopy confirm that these isolated DC present similar phenotypic and ultrastructural features to human thymic DC in situ and in culture. Purified DC, used as stimulator cells in mixed leucocyte reaction (MLR), induce stronger proliferative responses than peripheral blood monocytes used as a control; blocking assays with OKIa1 mAb plus complement greatly reduced this stimulatory potency. These functional assays demonstrate that we obtained a purified typical DC population that can be used in immunological functional studies to elucidate the specific role of DC in human thymus.

Modulation of Sertoli cell functions in the two-chamber assembly by peritubular cells and extracellular matrix

A two-chamber assembly has been employed to investigate influences of peritubular cells (PC) and extracellular matrix (Matrigel) on barrier formation by Sertoli cells (SC) in culture and on transferrin production. The kinetics of transport of [3H]inulin across a Millipore filter were essentially the same in the presence or absence of Matrigel or PC. In contrast, a SC monolayer retarded the diffusion of [3H]inulin, increasing the estimated time for 50% equilibration from about 4 h to approximately 12 h. Matrigel and PC each independently further increased the equilibration time, with the largest effects elicited by the presence of Matrigel (approximately 21 h). Data have been interpreted to indicate that these two components, especially extracellular matrix, facilitate the formation of a functional barrier by SC in the two-chamber system. PC assume a more important role than Matrigel in the modulation of transferrin secretion by SC. Transferrin concentrations were higher in the inner chamber, corresponding to those in the adluminal compartment, but transferrin masses were higher in the outer chamber under the conditions described. We report the effects of the presence and absence of Matrigel, PC, and FSH on levels of transferrin secreted by SC. Addition of FSH resulted in increased transferrin secretion by SC maintained under all conditions examined. We compare our data with those previously reported by others and attempt to provide a basis for the differences observed. We discuss the properties of the system and outline major advantages and limits of the two-chamber assembly in investigations on the polarity and properties of SC in culture.

Pleiotropic effects of the Bcg gene. I. Antigen presentation in genetically susceptible and resistant congenic mouse strains

The Ag-presentation ability of Bcgr and Bcgs spleen cells was studied in two sets of Bcg-congenic systems; namely, the BALB/c-BALB/c.Bcgr pair and the B10.A-B10.A-Bcgr pair, by using three sonicated soluble bacterial Ag (mycobacterium bovis bacillus Calmette-Guérin, Salmonella typhimurium, and Brucella abortus) as well as a particulate Ag (heat-killed Escherichia coli). Pulsed Bcgr spleen cells were shown to induce a stronger proliferation of the T cell-indicator system than their Bcgs counterparts. No difference in Ag-presenting ability could be shown between Bcgr and Bcgs peritoneal macrophages from normal animals. However, elicited peritoneal macrophages from immune Bcgr mice were superior in their Ag-presentation ability. Differences at the level of Ag presentation of Bcgr and Bcgs splenic cells were investigated further. Depletion of T cells and B cells did not alter the differences in Ag-presenting ability between Bcgr and Bcgs spleen cells. Furthermore, splenic dendritic cells of Bcgr or Bcgs allelic types were equally efficient in presenting bacillus Calmette-Guérin Ag to accessory cell-depleted T cells. In a final experiment, it was shown that spleen macrophages were the cell type involved in the superior Ag presentation by Bcgr splenic cells.

Pleiotropic effects of the Bcg gene. I. Antigen presentation in genetically susceptible and resistant congenic mouse strains

The Ag-presentation ability of Bcgr and Bcgs spleen cells was studied in two sets of Bcg-congenic systems; namely, the BALB/c-BALB/c.Bcgr pair and the B10.A-B10.A-Bcgr pair, by using three sonicated soluble bacterial Ag (mycobacterium bovis bacillus Calmette-Guérin, Salmonella typhimurium, and Brucella abortus) as well as a particulate Ag (heat-killed Escherichia coli). Pulsed Bcgr spleen cells were shown to induce a stronger proliferation of the T cell-indicator system than their Bcgs counterparts. No difference in Ag-presenting ability could be shown between Bcgr and Bcgs peritoneal macrophages from normal animals. However, elicited peritoneal macrophages from immune Bcgr mice were superior in their Ag-presentation ability. Differences at the level of Ag presentation of Bcgr and Bcgs splenic cells were investigated further. Depletion of T cells and B cells did not alter the differences in Ag-presenting ability between Bcgr and Bcgs spleen cells. Furthermore, splenic dendritic cells of Bcgr or Bcgs allelic types were equally efficient in presenting bacillus Calmette-Guérin Ag to accessory cell-depleted T cells. In a final experiment, it was shown that spleen macrophages were the cell type involved in the superior Ag presentation by Bcgr splenic cells.

Demonstration of OKT6 antigen on human thymic dendritic cells in culture

In situ, two types of dendritic cells (DCs) have been characterized in more detail: the interdigitating DCs of peripheral lymphoid tissues and the epidermal Langerhans cells. In order to characterize human thymic DCs, normal human thymus specimens were obtained from children undergoing cardiovascular surgery. In culture, DCs could be easily differentiated from macrophages and epithelial cells by their long fine processes, irregular nucleus, and dark, membrane-bound granules. By immunoelectron microscopy, using the protein A-gold and the avidin-biotinperoxidase complex techniques, cultured DCs were strongly labeled with anti-Ia and anti-OKT6 monoclonal antibodies. These results demonstrate that the phenotype of thymic DCs is similar to that of epidermal Langerhans cells and suggest that they may belong to the same cellular lineage.

Trends in hepatitis B surface antigen (HBsAg) prevalence in volunteer blood donors in Connecticut, 1973-1983

A total of 1,573,769 blood donations from volunteer blood donors from Connecticut were tested for Hepatitis B Surface Antigen (HBsAg) from 1973 to 1983. The prevalence of HBsAg decreased over this 10 year period among first time as well as repeat donors. This decrease was much more pronounced in the first three years of the study (1973 to 1975) in repeat donors. Thereafter, prevalence was stable. In first-time donors, the largest decrease also occurred in the first three years. In contrast to repeat donors, however, marked fluctuations in the prevalence were noted in first time donors. As has been the case in previous studies, HBsAg prevalence in first-time donors was significantly higher than that observed in repeat donors. Our study encompasses the longest period of observation in comparison to previous reports on HBsAg prevalence among blood donors. While it has been previously established that a decrease in prevalence over time does occur among repeat donors, stabilization of prevalence after an initial reduction found in our study has not been previously documented. This may indicate an irreducible minimum prevalence rate in the repeat donor population. In addition, our study for the first time convincingly demonstrates a reduction in prevalence in first-time donors which may reflect better communications at the donor recruitment and nursing level.

Characterization of human thymic dendritic cells in culture

Cells with dendritic shape, the so-called dendritic cells (DCs), have been described in many tissues. In order to characterize one DCs population, normal human thymus specimens were obtained from children undergoing cardiovascular surgery. These specimens were either put in culture or fixed for in situ ultrastructural, immunocytochemical and cytochemical studies. In culture, DCs could be differentiated from other non-lymphoid cell populations. They presented long, fine processes and an irregular nucleus. Like interdigitating cells (IDCs) in situ, their cytoplasm contained many free ribosomes and mitochondria, and a well-developed endoplasmic reticulum and Golgi complex. They showed a variable number of tubulovesicular structures and membrane-bound dark homogeneous granules. They never displayed phagolysosomes, tonofilaments or desmosomes. They were Ia+, ATPase+, S-100 protein+, vimentin+, esterase-, lysozyme-, and cytokeratin- cells. Macrophages were easily identified by their numerous lysosomes and large phagolysosomes. They were esterase+, lysozyme+, vimentin+, ATPase +/-, S-100 protein- and cytokeratin-. Although they were Ia+, membrane labelling was not as important as on DC's membrane. In situ, S-100 protein-positive cells had a dendritic shape and were located mainly in medullary regions and at the cortico-medullary border. The staining was diffused both in the nucleus and in the cytoplasm. Lysozyme-positive cells were randomly distributed in the cortex, the medulla and the connective septa. They were round cells and the staining was intracytoplasmic. These observations demonstrate that DCs can be isolated in human thymic cultures, and they suggest that these cells correspond to IDCs in situ. They also provide evidence to suggest that DCs and macrophages are two distinct cellular populations.

Control of the Bcg gene of early resistance in mice to infections with BCG substrains and atypical mycobacteria

The effect of the Bcg gene on the early host response to intravenous infection with a variety of BCG substrains and some atypical mycobacteria was investigated. The numbers of live bacilli of BCG Pasteur and BCG Tice recovered from the spleens of Bcgs mice (C57BL/6, B10.A and BALB/c) at 3 weeks following infection exceeded the bacterial dose injected, whereas the number of CFU recovered from the spleens of Bcgr mice (A/J, DBA/2 and C3H/HeN) did not exceed the number of CFU injected, thus following the pattern observed in Bcgr mice and Bcgs infected with BCG Montreal. BCG Russia failed to multiply in both test groups; however, the number of CFU recovered in Bcgr mice was significantly lower than in Bcgs mice. On the other hand, the presence of live bacilli in the spleens of either Bcgr or Bcgs mice injected with BCG Japan was undetectable in most cases. Involvement of the Bcg gene in the early resistance to infection with BCG Pasteur, BCG Russia, Mycobacterium kansasii and M. intracellulare was documented by the significant differences in the kinetics of infections in mice of the C.D2 (BALB/c-Bcgr) and BALB/c (Bcgs) congenic lines. In BCG Russia, M. intracellulare and M. fortuitum infections, the phenotypic expression of the Bcg gene resulted in a more rapid elimination of the bacteria in the spleens of Bcgr when compared with Bcgs mice. On the other hand, the hepatic granuloma formation correlated with bacterial load except when C.D2 mice were infected with a small dose of BCG Pasteur or M. kansasii where extensive granulomatous hepatitis developed although no bacterial multiplication occurred in the spleen. It is suggested that granuloma formation could depend of the properties of the mycobacteria as well as the genetic background of the host without implicating the bacterial burden.